Secondary power-producing cell

ABSTRACT

A secondary power-producing cell consists of an anode and a cathode formed of binary compounds containing the same two elements in different stoichiometric proportions, the electrodes being separated by an electrolyte containing ions of the element that is to be transported therethrough. During operation ions of the electropositive component of the electrode compounds transfer through the electrolyte from the anode to the cathode until the concentration thereof in the cathode approaches that in the anode. At this time the cell voltage decreases and the cell must be regenerated. The electronegative component of the cathode compound is then distilled from the cathode to the anode. Polarity of the electrodes is thereby reversed and operation of the cell may be resumed. For example the anode may be Li3P, the cathode Li2P5 and the electrolyte may be the LiF-LiC1-LiI eutectic.

0 United States Patent 1111 3,615,828

72 Inventor Albert K. Fischer 1,980,606 11/1934 Almeidas 136/20 [211 A lN ltyleztsn Springs, 111. 3,419,435 12/1968 Recht et al.... 136/6 pp o.3,492,160 1/1970 Silver 136/6 [22] Filed Mar. 9,1970 4s Patented on. 26,1971 :"i' g 'i gflji g' [73] Assignee The United States otAmerlcals 7 2;e

represented by the United sum Atomic Energy Commission ABSTRACT: Asecondary power-producing cell consists of an anode and a cathode formedof binary compounds containing the same two elements in differentstoichiometric proportions, [54] SECONDARY w p o CELL the electrodesbeing separated by an electrolyte containing mm 1 Dnwing 5 10118 of theelement that is to be transported therethrough. 52 U 8 Cl Duringoperation ions of the electropositive component of the l D l ndcompounds t f th h the le tro|yte from 136/20 the anode to the cathodeuntil the concentration thereof in the III- Cl. m. athode approachesthat in the anode At time the cc" 0f Sel'ch 20, ltage d r e and the cmust be regenerated The elec. 83116411611001, 24130125 tronegativecomponent of the cathode compound is then distilled from the cathode tothe anode. Polarity of the elec [56] References Cited trodes is therebyreversed and operation of the cell may be UNITED STATES PATENTS resumed.For example the anode may be Lid, the cathode 1,182,513 5/ 191 6 hlltofel1r r1.. 136/20 Li and the electrolyte may be the LiF-LiC l-Lileutectic.

PATENTEDnm 2s mu 3 r 3,615,828

I 12 z/e/zwf fllbert 15 Fischer SECONDARY POWER-PRODUCING CELLCONTRACTUAL ORIGIN OF THE INVENTION The invention described herein wasmade in the course of, or under, a contract with the U.S. ATOMIC ENERGYCOM- MISSION.

BACKGROUND OF THE INVENTION This invention relates to a device forgenerating electricity in a sealed, self-contained unit, using only anexternal heat source. In more detail the invention relates to anelectrochemical, power-producing cell and to a method of operating thiscell. In still more detail the invention relates to a polarityalternating thermally regenerative, electrochemical, power-producingcell.

In our technologically oriented society, there is an increasing need forcompact, convenient, pollution-free electrical power sources andenergy-storage devices. A large number of power-source needs, bothcivilian and military, have gone unfulfilled because of the limitedcapabilities of presently available batteries and engine generators. Inan attempt to satisfy these needs, a great deal of effort has beenexpended over the last decade in the areas of energy conversion andenergy storage. A large portion of the effort has involvedelectrochemical devices such as fuel cells, metal/air cells, secondary(electrically rechargeable) cells with both aqueous and nonaqueouselectrolytes and thermally regenerative cells.

Although a wide variety of electrochemical cells have been suggested forsuch purposes as long-lived spacecraft power supplies, militarycommunications uses, vehicle propulsion and off-peak energy storage forcentral stations, none have yet proven completely practical. Whiledevelopment of electrochemical cells for such purposes continues, it isprobable that the utility of these cells will, at least for the nearfuture, be restricted to specialized applications where there is a needfor power at almost any price. One such specialized utility is undercircumstances, probably in a remote location in an emergency situation,where heat is available but electrical energy is also needed. Noelectrochemical cells presently available are completely satisfactoryfor this purpose. Accordingly, a search for other cell configurationswhich are capable of satisfying this need must continue. Of course, anycell designed to fit such a specialized need may in fact have much widerapplicability and be useful more generally as noted above.

SUMMARY OF THE INVENTION An electrochemical power-producing cellaccording to the present invention includes an anode and a cathode whichcontain compounds formed of the same two elements in differentstoichiometric proportions and an electrolyte separating the electrodes.Regeneration of the cell is by heating the cathode to distill a portionof the electronegative component thereof over to the anode. Operation ofthe cell can then be continued with reversed polarity of the electrodes.

BRIEF DESCRIPTION OF THE DRAWING The single FIG. of the drawing is asketch showing a thermally regenerative, electrochemical cellconstructed in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing acathode consisting of a phosphorus-rich phosphide such as Li m-and ananode 11 consisting of a metal-rich phosphide such as Li are separatedby an electrolyte 12 such as the LiF-LiCl-Lil eutectic containing l 1.7mol percent LiF, 29.1 mol percent LiC, and 59.2 mol percent Lil meltingat 34lC. Current leads l3 and 14 are connected to the electrodes 10 and11 in conventional fashion. Electrodes 10 and 11 are also placed intocommunication by passageway 15 provided with a valve 16. Insulation, ofcourse, as necessary is employed.

During current generation valve 16 is closed, ions of theelectropositive component of the electrode compounds migrate from anodeto cathode and the concentration of this element in the cathodeapproaches that in the anode. Ultimately the cell voltage decreases toan unusable value and regeneration or recharging" of the cell isnecessary. This is accomplished by opening valve 16 and heating thecathode to distill phosphorous from the cathode to the anode throughpassageway 15. Condensation of phosphorous in the anode makes itphosphorous rich and the cathode metal rich. Thus, reversal of polarityoccurs and the former anode becomes the cathode and the former cathodebecomes the anode for continued generation of electric current.Operation of this cell is at about 350 C. and regeneration is at about800 C.

A wide variety of anode and cathode compounds and of the electrolyteused therewith may be used in practicing this invention. The onlyrequirement on the electropositive element of the electrode compounds isthat it be an element that can form two or more binary compounds ofdifferent stoichiometries with the electronegative component. Inaddition to a similar requirement on the electronegative component, itmust be distillable at a reasonable temperature. Thus theelectropositive component of the electrode compounds may be chromium,iron, lithium, sodium, cadmium,

Anode Cathode Electrolyte Cr P CrP, CrCl, solution in KCl-NaCl Cd l Cd!CdCl, in KCl (m.p. 380-390 c.) 11,? Fe,P FeF, in HF (m.p. 360C.) Zn P,ZnP, ZnCl (m.p. 262 C.) or

ZnCh-KCI (m.p. 228 c.) Cu P Cu,P CuCl in KCl (m.p. C.)

Persons skilled in the art will, of course, readily adapt the generalteachings of the invention to embodiments far different than theembodiments illustrated. Accordingly, the scope of the protectionafforded the invention should not be limited to the particularembodiment illustrated in the drawings and described above, but shouldbe determined only in accordance with the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A secondary, power-producing cell comprising an anode and a cathodeeach consisting of ;binary compounds containing the same two elements indifferent stoichiometric proportions wherein the electropositivecomponent of the electrode is chromium, iron, lithium, sodium, cadmium,copper or zinc and the electronegative component is phosphorus,selenium,

tellurium, sulfur, arsenic, or nitrogen said anode being rich in theelectropositive component and said cathode being rich in saidelectronegative component and an electrolyte that contains ions of theelement that is to be transported through it separating the electrodes,said electronegative component being distillable.

2. A secondary power-producing cell according to claim 1 and includingmeans for heating the cathode and for transferring the electronegativecomponent thereof to the anode.

3. A secondary power-producing cell according to claim I wherein theanode is Li P, the cathode is Li P and the electrolyte is the LiF, LiCl,LiI eutectic.

4. A method of operating a secondary power-producing cell as in claim 1comprising operating the cell near to discharge, heating the cathode todistill the electronegative component of the cathode material, over tothe anode to reverse the polarity of the cell and continuing operationof the cell with reversed polarity of the electrodes.

2. A secondary power-producing cell according to claim 1 and includingmeans for heating the cathode and for transferring the electronegativecomponent thereof to the anode.
 3. A secondary power-producing cellaccording to claim 1 wherein the anode is Li3P, the cathode is Li2P5,and the electrolyte is the LiF, LiCl, LiI eutectic.
 4. A method ofoperating a secondary power-producing cell as in claim 1 comprisingoperating the cell near to discharge, heating the cathode to distill theelectronegative component of the cathode material, over to the anode toreverse the polarity of the cell and continuing operation of the cellwith reversed polarity of the electrodes.